Generally, brake systems of motor vehicles are hydraulic brake systems that act on all wheels of the motor vehicle involved in a braking event. In particular, a master cylinder is operated with a brake pedal and pressure is generated in a pressure chamber filled with brake fluid. The brake fluid is passed by way of hydraulic lines to wheel brake cylinders associated with each wheel of the vehicle. Under pressure of the brake fluid, brake linings of brake pads come into contact with a respective brake drum or brake disk. This pressure is a braking force acting on the wheel connected to the drum or brake and may be monitored. In some instances, a brake booster may be provided to increase the braking force.
Different brake pressures, forces, torques may be applied to the individual wheels of the vehicle or even to wheels of the front axle and the rear axle, in order to achieve an optimal braking effect where there may be different loads on the front and rear axles. Different brake torques may be fixedly specified by correspondingly different configurations of the braking mechanisms of the front and rear axles and may also be influenced by correspondingly different settings of the brake pressures that are applied to the braking mechanisms of the front and rear axles.
A constant goal in brake system improvement has been to achieve high braking deceleration. Known braking control systems determine signals from an axle load signal that correspond to a static component and a dynamic component of the axle load. From the axle load signal and a signal produced by the brake pedal, a first brake pressure control signal is generated. A second brake pressure control signal may be superimposed depending on the axle load, to control the brake pressure.
Known braking control systems also distribute brake load from one wheel brake to another wheel brake in the event a monitoring signal of one wheel brake indicates a high temperature or wear of the brake lining of one particular brake. It is also known to reduce brake pressure at the rear axle during a braking event when a braking process is compared to a static load in order to set the same adhesion utilization on the front axle and the rear axle.
Vehicle brake systems are being improved to achieve high braking deceleration as a significant safety factor in collision avoidance. However, a high braking deceleration produces a pitching motion of the motor vehicle, producing a physical load for occupants of the vehicle, especially relevant to neck muscles, which may be highly stressed in order to keep the head up while compensating for the pitching motion. A headrest on the vehicle seat may alleviate some pitch angle for the driver.
Pitching motion of the vehicle may be particularly problematic in vehicles equipped with an autonomous brake system. In an autonomous brake system the braking event is automatically initiated by an emergency braking system. Because the driver may not be expecting the braking event, the driver may not be prepared for the pitching motion and may not have time to tension their neck muscles in anticipation of the pitching motion. Furthermore, the uncomfortable effect of pitching motion of a motor vehicle may cause the driver to select a lower braking deceleration than appropriate for a particular traffic situation possibly compromising safety.
A system and method of operating a brake system of a motor vehicle is needed to alleviate pitching motion of the motor vehicle caused by the braking process.